This invention relates to an solenoid coil bobbin for an electromagnetic switch of a starter, and specifically to an insulating construction of a lead wire portion.
A conventional electromagnetic switch of a starter is explained with respect to FIG. 3. An exciting coil 1 is wound around a bobbin 10. A rigid iron core 3 supports the bobbin 10. A case 2 holds the rigid iron core 3 as a yoke. A plunger 5 consisting of a magnetic material is held on the front inner surface of the case 2, slidable along the axial direction thereof, and is provided with a rod 6 at the rear end portion thereof as one body. A movable contact 7 is fixed to the rear end portion of the rod 6 in an insulated manner. A pair of fixed contacts 8 is positioned corresponding to the movable contact 7 in the axial direction. A hook 9 is held in the bore of the plunger 5 and is slidable along the axial direction. The front end portion of the hook is in contact with the top portion of a shift lever 9a so as to rotate the lever.
The operation of the conventional electromagnetic switch thus constructed will be described. When the exciting coil 1 is turned on, the plunger 5 is attracted to the rigid iron core 3, and the hook 9 is moved back. Further, the shift lever 9a is rotated so as to link a pinion of a rotating axis of an armature with a ring gear of an engine (not shown). Next, the movable contact 7 closes the pair of fixed contacts 8 so as to start to rotate the starter.
The exciting coil 1 is constructed from an outer coil 1a and an inner coil 1b wound around the bobbin 10 consisting of a synthetic resin (e.g. nylon reinforced by grass-fiber).
The conventional solenoid coil bobbin (Japanese Patent Publication No. sho. 63-8087) will be described with reference to FIG. 4a, and FIG. 4b.
The bobbin 10 is provided with a cylindrical part 12 and flanges 13 and 14 projecting toward the radial direction of the cylindrical part 12 at the both side ends of part 12 so as to define each edge wall of the bobbin. The flange 14 is provided with two notches 15 on the circumferential edge thereof as an inlet for wire passage when beginning to wind the coils 1a and 1b. Moreover, the flange 14 is provided with lead wire elements 18 having a cylindrical shape and projecting from an axial outer surface thereof, with circumferential walls 17 of the lead wire parts 18 provided with line openings 16 along the axial direction thereof and being connected with the notches 15, respectively.
The two lead wire elements 18 have the same structure. Namely, an axial partition 19 which has a narrow width than the line opening 16 is provided in the circumferential wall 17 and projects in the radial direction of the flange 14, so as to form circumferentially adjacent axial grooves 20a and 20b. Each of grooves 20a and 20b is open to the line opening 16 of the wall 17, and connected with one of the notches 15 of the flange 14.
The wall 17 of the lead wire part 18 is constructed from a large diameter part 17a on a side thereof toward flange 14 and a small diameter part 17b projecting in an axial outer direction from the large diameter part 17a. The difference between the large diameter part 17a and the small diameter part 17b is only the diameter, each width value of the grooves 20a, 20b and partition 19 is same in both of the parts 17a and 17b. The small diameter part 17b of the wall 17 is provided with a width slit 17c which connects the groove 20a with a circumferential surface of the small diameter part 17b. Moreover, a circumferential surface of the large diameter part 17a of the wall 17 is provided with projections 16a and 16b disposed on the edges of the line opening 16. The above-mentioned parts consist of synthetic resin as one body.
In the above mentioned bobbin, after winding the inner coil 1b, the outer coil 1a with its lead wire (not shown) is passed through the groove 20a (shallow side) wound around the inner coil 1b. After this, the projections 16a and 16b disposed along the edges of the line opening 16 of the lead wire part 18 are bent to the inside of the opening by heat softening so as to close the line opening 16. As a result of closing, the large diameter part 17a of the circumferential wall of the lead wire part 18 would not only have a surface without discontinuous portions, but also prevent escape of the lead wire from the grooves 20a and 20b. The constructed lead wire part 18 is inserted in a wall of the rigid iron core 3 of the electromagnetic starter 2 using the bobbin.
The above bobbin of the conventional electromagnetic switch has a problem in that the producing processes for providing the projections 16a and 16b on each edge of the grooves 20a and 20b are expensive and in that bending the projections 16a and 16b by heat softening increases the production period and expense.